Generally, sprinklers are fire fighting equipment installed on the ceilings of buildings for spraying extinguishing liquid, or water, upon sensing the occurrence of a fire, so as to extinguish the fire.
A typical sprinkler head H comprises, as shown in FIG. 9, an extinguishing liquid discharging nozzle 1 coupled with an extinguishing liquid supply pipe 33 via a pipe of the discharging nozzle 1, an extinguishing liquid diffusing plate 6 fitted horizontally under and to the lower end of the O-ring-shaped body 2, a valve plate 3 for normally holding the discharging nozzle 1 closed, a trigger 4 installed within a space between the valve plate 3 and the bottom of the body 2 for supporting the valve plate 3, and a thermal fuse 7 installed within the trigger 4. The thermal fuse F includes, as shown in FIG. 10, a hollow drum-shaped casing 11 enclosed at its bottom, low-temperature fusing lead 13 filled within the casing 11 and held solid at room temperature, and an actuating pin 12 held within the lead 13 at its lower end and projected out of the top of the casing 11 at its upper end. As the ambient temperature rises due to the occurrence of a fire, the low-temperature fusing lead 13 in the thermal fuse 7 fuses to become a liquid state, thereby causing the actuating pin 12 to be sunk in the lead 13 and thus the valve plate supporting balance of the trigger 4 to be broken. As a result, the valve plate 3 opens the extinguishing liquid discharging nozzle 1 to spray extinguishing liquid.
There has been proposed another conventional sprinkler wherein a glass ampule (not shown) filled with a temperature-expansive gas is provided instead of the above low-temperature fusing lead-type thermal fuse. If a fire occurs, then the gas in the glass ampule expands to break the glass ampule, thereby causing a valve plate supporting force to be lost. This sprinkler is substantially the same in operation as that with the low-temperature lead thermal fuse.
On the other hand, the above-mentioned conventional sprinklers using either the low-temperature lead fuse or temperature-expansive glass ampule have such a structure that the fuse or glass ampule reacts directly to substantial heat of a fire. In this regard, such conventional sprinklers are disadvantageous in that they have a very slow response to the initial stage of a fire because they are not actuated in the event of the fire until the ambient temperature reaches a fusing point of the low-temperature lead or an expansion-breaking point of the glass ampule. In connection with such a problem, U.S. Pat. No. 2,245,144, invented by William B. Griffith, et al., shows a technique for breaking or melting the glass ampule or low-temperature lead fuse using not the fire heat but electric heating means. In this patent, as shown in FIG. 11, in the event of a fire, a diaphragm (41 in the patent) first expands at a low temperature prior to the melting of the fuse and then applies electric power to an electric heating coil (20 in the patent) around the fuse or glass ampule. In this technique, the diaphragm functions as a mechanical temperature sensor expanding when the ambient temperature exceeds a predetermined threshold value and also as an electrical switch for applying electric power to electric heating means (electric heating coil) upon the expansion.
Another approach to using the electric heating means around the fuse or glass ampule is shown in International Application No. PCT/FI93/00164 (International Publication No. WO 93/21998), inverted by Sundholm, Göran. In this publication, as shown in FIGS. 12a, 12b and 12c, an electric heating coil (8 in the publication) of memory metal is laid around the glass ampule. The memory metal coil is held contracted at room temperature to hold an electric circuit opened (see FIG. 12a). When the ambient temperature reaches a predetermined threshold value due to the occurrence of a fire, the memory metal coil changes (or expands) its shape to function as a switch for closing the electric circuit. After closing the electric circuit, the memory metal coil functions as the electric heating means for heating the fuse or ampule. For reference, FIG. 12b shows a state where the memory metal coil expands and makes an electrical connection to act as a heater, and FIG. 12c shows a state where a spindle (5 in the publication) is pressed downwardly (to spray extinguishing liquid) under the influence of a spring (6 in the publication) after the glass ampule is broken.
The sprinklers shown in the '144 patent and '21998 publication comprise the electric heating means for heating the fuse or glass ampule at a predetermined low temperature before the substantial fire heat reaches the fuse or glass ampule. In this regard, such sprinklers are advantageous in that they have a faster response to the initial stage of a fire than that of the conventional sprinklers using the glass ampule or fuse breaking or melting due to the direct heating by the substantial fire heat. However, such sprinklers still have the following disadvantages.
Firstly, because fire fighting equipment such as sprinklers is at present installed in almost all buildings but provided only against an emergency such as the occurrence of a fire, it is mostly left unused for a lengthy period of time due to the event of no fire. As a result, the fire fighting equipment may be aged or damaged partially in its electric circuit due to insincere maintenance, finally becoming a useless thing in the actual event of a fire. In order to solve this problem, there is a need to frequently test the operations of the sprinklers. However, it is not easy to frequently test a large number of sprinklers installed on the ceiling.
Secondly, in almost all cases, a fire occurs beginning with a certain local place, and only a sprinkler installed in that local place is actuated and sprinklers installed in other rooms adjacent thereto are not actuated, thereby making it impossible to prevent the fire from being spread toward the adjacent rooms. On the other hand, in the previously stated '144 patent, another switching means (37 in the patent) is provided in addition to the diaphragm-type mechanical/electrical switching means to manually close the electric circuit. The provision of such switching means may establish manual electrical connections to sprinklers in other places than a place where a fire occurs, as needed. However, this '144 patent does not show any means (for example, means for connection between sprinklers, means for acquiring information needed for an operator's operation, command transfer means, etc.) embodied for controlling individual electrical connections to the respective sprinklers.